Looks like a sore of some sort, maybe a cricket bite? You can put some Neosporin on it to help prevent infection. Keep an eye on it and make sure it heals and his foot does not swell.
It's a wound of some kind.
Do be sure to keep it clean, and monitor your cham close.
Even a small wound, if infection sets in, can rapidly spread through your
cham's body.
Is it bleeding, or is there a scab where it was bleeding?